1. Field of the Invention
This invention relates to compressed air systems for providing compressed air powered tools and equipment with air from a reservoir in which the reservoir is served by two or more compressors which are activated sequentially in response to the air pressure in the reservoir.
2. Description of Related Art
Manufacturing facilities often use compressed air as means to power tools, conveyers, machines, presses, and other production equipment, henceforth designated "machinery". Compressed air customarily is produced by a compressor or compressors at a central point, stored in a reservoir, and piped to the production equipment.
The demand for compressed air often varies radically over a working day, with fluctuations reflecting rest breaks, lunch periods, and the start-up or shut-down of production lines.
In order to meet a fluctuating demand for compressed air, two or more compressors are used, with the base compressor or compressors in operation constantly, and a trim compressor activated when demand reaches a preset level, as indicated by a decline in the air pressure in the reservoir to a minimum level. The number of base compressors may vary from 1 to as many as 9 or more, depending on the level of demand for compressed air. In all plants excess capacity is designed into the compressed air system, i.e. the compressed air production of the base and trim compressors combined exceeds the maximum demand for compressed air by the machinery.
Such an operation is often inefficient as the trim compressor may be activated and shortly thereafter unloaded to meet a small or transient increase in compressed air demand. Activation of a trim compressor to meet a small demand for compressed air is inefficient with respect to power consumption, a very large expenditure of power is required to meet a small demand for compressed air. In addition, activation is expensive in terms of wear on the trim compressor and associated maintenance and replacement costs.
This invention is a system which accommodates momentary fluctuations of demand without the expensive activation of a trim compressor.
U.S. Pat. No. 2,512,043 discloses a system in which compressed air is supplied from a reservoir which is replenished by a compressor. If a momentary demand causes a drop of the air pressure in the reservoir, the system automatically draws compressed air from an emergency reservoir, which is then replenished by the compressor.
U.S. Pat. No. 2,791,230 discloses apparatus for automatically insuring a continuous supply of gas from a series of cylinders. The cylinders are exhausted of gas sequentially. The system involves an arrangement of cylinders, tubing, and valves in which the electrical sensing of decreased pressure in a cylinder energizes a solenoid valve which opens a reserve cylinder.
U.S. Pat. No. 3,807,422 discloses a system in which a single compressor is used to charge a series of tanks. The system maximizes the available pressure in the tanks by charging the tank with the highest residual pressure first and withdrawing from the tanks with the lowest residual pressure first.
U.S. Pat. No. 4,597,406 discloses a device for delivery of gas under constant pressure from either of two vessels. The output gas pressure is controlled by a single pressure regulator. The system is designed to supply the output from one operative vessel while the other is on standby. Electrical switches and valves control the connection of each vessel with the output line.
The prior art disclosures do not achieve the function of the present invention, that of providing machinery with an adequate supply of compressed air at a satisfactory pressure while minimizing the consumption of power by the trim compressor.